Engineering Conductivity and Performance in Electrorheological Fluids Using a Nanosilica Grafting Approach

Carbonization is considered an effective process forthe preparationof carbon-rich solids for various applications. Raw carbonaceous particleshowever often possess high electrical conductivity, limiting theirapplicability in electrorheology. To address this drawback, the carbonaceousparticles prepared from glucose through hydrothermal synthesis, followedby thermal carbonization in an inert atmosphere, were subsequentlycoated by compact and mesoporous nanosilica, giving rise to semiconductingparticles. The successful coating was confirmed using transmissionelectron microscopy and spectroscopic analysis, and the compositeparticles were further used as a dispersed phase in electrorheological(ER) fluids of concentration 5 wt %. While an ER fluid based on purecarbonized particles caused a short circuit of the measuring deviceat the electric field of intensity 1 kV mm(-1), theER behavior of its analogue based on mesoporous silica-coated particleswas successfully measured up to 3 kV mm(-1), givinga high yield stress exceeding even the values estimated for ER fluidsbased on similar carbonaceous particles coated with a compact silicalayer. Even though the conductivity decreased only about one orderof magnitude after the coating process, the dielectric propertiesof the prepared ER fluid differed significantly, the relaxation processwas shifted to lower frequencies, and most importantly, the dielectricrelaxation strength increased, indicating an increased amount of interactions.The presence of mesoporous nanosilica further enhanced the sedimentationstability of the ER fluids when compared to its analogue with thecompact silica coating, expanding the scope of practical applicability.